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maxw55276389
Participant
November 14, 2018
Question

Advanced Lens Corrections

  • November 14, 2018
  • 2 replies
  • 6118 views

Dear community,

I am looking for a way to remove the lens distortions of a gorpo hero 7 black. I know that one can use the "optics compensation" effect to remove the fisheye distortion. It does work pretty well. However, when I use a stabilization procedure (Mercalli prodad) afterwards, I can still see that the image has slight distortions in it. This is because the image stabilization shifts the frames all the time and even the slightest position-dependent distortions become visible. It is as if the remaining distortions are moving within the video.

So what I want is actually a more advanced lens distortion correction which can eliminate distortions beyond fisheye. Can somebody help me or give me a hint? I would be very thankful for any advice.

I am using AE CC 2017.

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    2 replies

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    patrikj45960157
    Participant
    January 1, 2019

    Is this what you are looking for?

    https://community.gopro.com/t5/Cameras/GoPro-Hero-7-black-and-Adobe-Premiere-Pro/m-p/260843/highlight/true#M75734

    R
    Community Expert
    Rick GerardCommunity Expert
    Community Expert
    November 14, 2018

    Start by using GoPro studio to correct the footage and save it in the Cineform codec.

    Anything more advanced than that is going to require you to shoot a test grid and come up with your own correction factors. You can't just eyeball the correction.

    As far as workflow you have two options. Remove stabilize the original footage and then correct for distortion or correct for the distortion, render a DI (digital intermediate) and stabilize the DI.

    If you are doing composites or adding things to the frame that you want to look like are actually in the shot, it is usually better to do the tracking and compositing with the footage before it is "warp" stabilized, precompose the entire composite and then apply the stabilizer to the entire composite. That way the entire new image gets bent into the new shape to smooth out the action.

    M
    maxw55276389Author
    Participant
    November 14, 2018

    Hello Rick, thank you for the reply!

    GoPro Studio was discontinued. After a longish search I found an installation file on the internet which I will try out later. However, I'm not so sure whether this software is able to remove the distortions of the hero7 black, since GoPro Studio was discontinued way before the hero7 was released. I will give it a try though.

    Regarding the workflow: Image stabilization should always be applied after lens correction. Otherwise one will see moving distortions while the footage is actually stable. These moving distortions cannot be removed by a static lens profile. So lens corrections after image stabilization are useless. At least that's how I understand it.

    I'm glad that you mention a test grid. I had exactly that idea. But which effect should I use to straighten a reference grid? There is a tool called "Adobe Lens Profile Creator". Apparently is can compute a lens profile for an arbitrary lens by analyzing some frames with check board patterns. Can I use these profiles in AE?

    R
    Community Expert
    Rick GerardCommunity Expert
    Community Expert
    November 14, 2018

    maxw55276389  wrote

    Regarding the workflow: Image stabilization should always be applied after lens correction. Otherwise one will see moving distortions while the footage is actually stable. These moving distortions cannot be removed by a static lens profile. So lens corrections after image stabilization are useless. At least that's how I understand it.

    Not necessarily so. Image stabilizers work on predicting the motion of the edges of the detail in a shot. The most efficient approach depends on the shot. Rolling shutter correction is mathematical. It is not based on predicting the movement of pixels, it is based on the scan rate of the camera. With real problematic footage, I would do rolling shutter correction, pre-compose, perform lens correction, then, if tracking and compositing were required I would precompose or render a DI, track, and composite, then pre-compose the entire composite so that it could be stabilized. That way the warping required to stabilize the image would be calculated on the entire image.

    On the other hand, if you just wanted to do image stabilization and you no compositing was required, most of the time, you would have more information in the frame to work with so I would fix the rolling shutter, pre-compose, run image stabilization (Warp Stabilizer or equivalent) then pre-compose and perform the lens correction.

    The most efficient and most effective workflow depends entirely on the shot and the effects you want to apply to the shot. No one solution works for every shot and not every shot can be stabilized. If this was a crude handheld shot on a windy day it would be nearly impossible to stabilize:

    But this one would probably work just fine because there is at least something in the shot that is not moving:

    One workflow that will not work at all is applying lens correction as an effect and then running Warp Stabilizer (or other stabilization software) because the render order gets fouled up and you can't do anything about it.

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